1. Field of the Invention
The present invention relates to a phase adjustment circuit for adjusting the phases of a plurality of signals.
2. Description of the Related Art
To record information on a recordable optical disk medium, it is necessary to generate a special write waveform for suppressing interference of a write signal. This sometimes requires phase information that is finer than one-fortieth of the write data rate. For example, a 16x DVD system needs very short phase information with a resolution of about 50 psec.
In an optical disk drive and the like, a set of signals with fine phases generated by a signal processing LSI is usually transmitted through an output driver, such as an LVDS, to a write amplifier attached at the tip of the optical pickup (see, for example, Yoshiaki Konno et al., “A CMOS 1X- to 16X-Speed DVD Write Channel IC”, IEEE International Solid-State Circuits Conference, Feb. 9, 2005, pp. 568-569, 618).
In the case where the set of fine-phase signals is transmitted over a long distance, a problem arises in that when the signals reach the write amplifier, the phase relation among the signals collapses due to variation in delay in the signal lines and the like. To be specific, the signal processing LSI produced the set of signals whose phase should increase monotonously, but the monotonic phase increase collapses when the signals reach the write amplifier. As a result, in spite of control for increasing the pulse width of a write signal, for example, the actual write signal has a narrow pulse width, which results in degradation of the quality of the writing on the optical disk medium. As writing speed is expected to increase, there is concern that this kind of problem will become more serious in the future.